U.S. Pat. No. 5,539,990, which is wholly incorporated herein by reference, disclosesan optical levelling, plumbing and angle-calibrating instrument including a frame, a plumb body universally pendulously mounted on the frame and defining a vertical plumb line gravitationally, at least an illuminator electrically connected to a power supply and mounted on the plumb body for emitting laser light, and at least a cylindrical-surfaced lens mounted on the plumb body in front of the illuminator for planarly diverging the laser light as emitted from the illuminator through the lens to form a laser light plane transverse to a lens axis of the cylindrical-surfaced lens, whereby the laser light plane will projectively intersect an objective wall to form a straight line of optical image, serving as a reference line for levelling or plumbing use. Such laser level may be difficult to install on a wall, etc.
It is an object of the present invention to provide a laser level that is inexpensive and usable by the general public in multiple applications.